Merge branch '214-do-not-return-local-stack-address'

Use static string object for keeping the c_str message for the caller.
Strings collection used as an alternative to memory leaks done via strdup().
To add, TargetBufferSmallerThanSource Exception should never happen in a correctly written library client, as this completely depends on the implementation and not on the communication with the device

Downside: if missed and when occurring too often, the memory taken by the exception messages can take too much memory.
Potential improvement: replace std::vector with a kind of a ring buffer, or add simple wrapping logic over it.

This should avoid breaking ABI by using static memory. Note: there might be multiple exceptions' strings collections (for each compilation unit including this header).
Correct that for libnitrokey 4, by keeping string as a member of the exception.

Fixes #214
Fixes #217

CMakeLists.txt

@@ -104,7 +104,7 @@ set_target_properties(nitrokey PROPERTIES
 
 OPTION(ERROR_ON_WARNING "Stop compilation on warning found (not supported for MSVC)" OFF)
 if (NOT MSVC)
-    set(COMPILE_FLAGS "-Wall -Wno-unused-function -Wcast-qual -Woverloaded-virtual -Wsign-compare -Wformat -Wformat-security")
+    set(COMPILE_FLAGS "-Wall -Wno-unused-function -Wcast-qual -Woverloaded-virtual -Wsign-compare -Wformat -Wformat-security -Wreturn-local-addr")
     IF(NOT APPLE)
         if (ERROR_ON_WARNING)
             set(COMPILE_FLAGS "${COMPILE_FLAGS} -Werror")

libnitrokey/LibraryException.h

@@ -22,6 +22,7 @@
 #ifndef LIBNITROKEY_LIBRARYEXCEPTION_H
 #define LIBNITROKEY_LIBRARYEXCEPTION_H
 
+#include <mutex>
 #include <exception>
 #include <cstdint>
 #include <string>
@@ -32,6 +33,12 @@ class LibraryException: std::exception {
     virtual uint8_t exception_id()= 0;
 };
 
+// Use static string object for keeping the c_str message for the caller.
+// Strings collection used as an alternative to memory leaks done via strdup().
+// TargetBufferSmallerThanSource Exception should never happen in a correctly written library client.
+static std::vector<std::string> g_exception_messages;
+static std::mutex g_exception_message_mutex;
+
 class TargetBufferSmallerThanSource: public LibraryException {
 public:
     virtual uint8_t exception_id() override {
@@ -47,11 +54,12 @@ class TargetBufferSmallerThanSource: public LibraryException {
             ) : source_size(source_size_),  target_size(target_size_) {}
 
     virtual const char *what() const noexcept override {
+        std::lock_guard<std::mutex> lock(g_exception_message_mutex);
         std::string s = " ";
         auto ts = [](size_t x){ return std::to_string(x); };
-        std::string msg = std::string("Target buffer size is smaller than source: [source size, buffer size]")
-            +s+ ts(source_size) +s+ ts(target_size);
-        return msg.c_str();
+        g_exception_messages.emplace_back(std::string("Target buffer size is smaller than source: [source size, buffer size]")
+                              + s + ts(source_size) + s + ts(target_size));
+        return g_exception_messages.back().c_str();
     }
 
 };

libnitrokey/stick10_commands_0.8.h

@@ -131,7 +131,7 @@ namespace nitrokey {
                       std::stringstream ss;
 #ifdef LOG_VOLATILE_DATA
                       ss << "data:" << std::endl
-                         << ::nitrokey::misc::hexdump(reinterpret_cast<const uint8_t *>&data), sizeof data);
+                         << ::nitrokey::misc::hexdump(reinterpret_cast<const uint8_t *> (&data), sizeof data);
 #else
                       ss << " Volatile data not logged" << std::endl;
 #endif